Enable TYP_STRUCT LCL_VAR/LCL_FLD call args on ARM (#71598)

* ARM: local morph

* ARM: morph

* Jit dumps: print '(AX)' and others for LCL_FLD nodes

* Delete invalid assert

* Work around emitter limitations

Author: SingleAccretion

src/coreclr/jit/codegenarmarch.cpp

@@ -1235,9 +1235,6 @@ void CodeGen::genPutArgSplit(GenTreePutArgSplit* treeNode)
             assert(baseReg != addrReg);
         }
 
-        // We don't split HFAs.
-        assert(!compiler->IsHfa(layout->GetClassHandle()));
-
         // Put on stack first
         unsigned structOffset  = treeNode->gtNumRegs * TARGET_POINTER_SIZE;
         unsigned remainingSize = layout->GetSize() - structOffset;

src/coreclr/jit/gentree.cpp

@@ -10558,7 +10558,7 @@ void Compiler::gtDispNode(GenTree* tree, IndentStack* indentStack, _In_ _In_opt_
                 }
             }
 
-            if (tree->gtOper == GT_LCL_VAR || tree->gtOper == GT_STORE_LCL_VAR)
+            if (tree->OperIsLocal())
             {
                 LclVarDsc* varDsc = lvaGetDesc(tree->AsLclVarCommon());
                 if (varDsc->IsAddressExposed())

src/coreclr/jit/lclmorph.cpp

@@ -715,11 +715,11 @@ class LocalAddressVisitor final : public GenTreeVisitor<LocalAddressVisitor>
             unsigned   indirSize = GetIndirSize(node, user);
             bool       isWide;
 
-            if ((indirSize == 0) || (val.Offset() > UINT16_MAX))
+            if ((indirSize == 0) || ((val.Offset() + indirSize) > UINT16_MAX))
             {
                 // If we can't figure out the indirection size then treat it as a wide indirection.
-                // Likewise if we won't be able to tranform this indirection into a local node due
-                // the large offset.
+                // Additionally, treat indirections with large offsets as wide: local field nodes
+                // and the emitter do not support them.
                 isWide = true;
             }
             else
@@ -1035,56 +1035,12 @@ class LocalAddressVisitor final : public GenTreeVisitor<LocalAddressVisitor>
             indirLayout = indir->AsBlk()->GetLayout();
         }
 
-        // How does the "indir" match the underlying location?
-        //
-        enum class StructMatch
-        {
-            Compatible,
-            Partial
-        };
-
-        // We're only processing TYP_STRUCT variables now.
-        assert(varDsc->GetLayout() != nullptr);
-
-        StructMatch match = StructMatch::Partial;
-        if ((val.Offset() == 0) && ClassLayout::AreCompatible(indirLayout, varDsc->GetLayout()))
-        {
-            match = StructMatch::Compatible;
-        }
-
-        // Current matrix of matches/users/types:
-        //
-        // |------------|---------|---------|---------|
-        // | STRUCT     | CALL(*) | ASG     | RETURN  |
-        // |------------|---------|---------|---------|
-        // | Compatible | LCL_VAR | LCL_VAR | LCL_VAR |
-        // | Partial    | LCL_FLD | LCL_FLD | LCL_FLD |
-        // |------------|---------|---------|---------|
-        //
-        // * - On XArch/Arm64/LA only.
-        //
-        // |------------|------|------|--------|----------|
-        // | SIMD       | CALL | ASG  | RETURN | HWI/SIMD |
-        // |------------|------|------|--------|----------|
-        // | Compatible | None | None | None   | None     |
-        // | Partial    | None | None | None   | None     |
-        // |------------|------|------|--------|----------|
-        //
-        // TODO-ADDR: delete all the "None" entries and always
-        // transform local nodes into LCL_VAR or LCL_FLD.
-
-        assert(indir->TypeIs(TYP_STRUCT) && user->OperIs(GT_ASG, GT_CALL, GT_RETURN));
-
         *pStructLayout = indirLayout;
 
-        if (user->IsCall())
-        {
-#ifdef TARGET_ARM
-            return IndirTransform::None;
-#endif // TARGET_ARM
-        }
+        // We're only processing TYP_STRUCT uses and variables now.
+        assert(indir->TypeIs(TYP_STRUCT) && (varDsc->GetLayout() != nullptr));
 
-        if (match == StructMatch::Compatible)
+        if ((val.Offset() == 0) && ClassLayout::AreCompatible(indirLayout, varDsc->GetLayout()))
         {
             return IndirTransform::LclVar;
         }

src/coreclr/jit/morph.cpp

@@ -3127,8 +3127,8 @@ GenTreeCall* Compiler::fgMorphArgs(GenTreeCall* call)
                 // - For ARM and ARM64 it must also be a non-HFA struct, or have a single field.
                 // - This is irrelevant for X86, since structs are always passed by value on the stack.
 
-                GenTree* lclVar       = fgIsIndirOfAddrOfLocal(argObj);
-                bool     argIsLocal   = (lclVar != nullptr) || argObj->OperIsLocalRead();
+                GenTree* lclVar       = argObj->OperIs(GT_LCL_VAR) ? argObj : fgIsIndirOfAddrOfLocal(argObj);
+                bool     argIsLocal   = (lclVar != nullptr) || argObj->OperIs(GT_LCL_FLD);
                 bool     canTransform = false;
 
                 if (structBaseType != TYP_STRUCT)